1. Field of the Invention
The present invention relates generally to fluid reaction surfaces, and more specifically to a turbine blade with an internal cooling circuit.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine such as an industrial gas turbine (IGT) includes a turbine section with multiple stages of turbine blades that react with the hot gas flow passing through the turbine to convert the combustion gas flow into mechanical work to drive the compressor and the output shaft. The efficiency of the engine can be increased by passing a higher temperature gas flow through the turbine. However, the temperature limit of the hot gas flow entering the turbine is limited to the metal properties of the turbine blades, especially in the first stage. For this reason, the turbine blades are provided with complex internal cooling circuits to provide cooling of the blade so that the hot gas flow temperature can exceed the thermal properties of the blade.
Since the compressed air used to cool the blades is also bled off from the engine (from the compressor), the engine efficiency can also be increased by using a minimal amount of bleed off air to perform the maximum amount of blade cooling. The turbine blades can also be affected by erosion occurring from the hot gas flow in areas where hot spots can occur on the blade. Some areas on the blade may be over-cooled while other areas are under-cooled, leading to hot spots. Inadequate cooling of the rotor blades can also affect the amount of creep that can occur. In an IGT, the engine can operate non-stop for 24,000 to 48,000 hours before a shutdown will occur. Because the rotor blades are operating under very high temperatures and are exposed to high stress levels from the rotation of the engine, the metallic material can become plastic and distort in the direction of the high centrifugal forces. Thus, it is highly desirable to provide for adequate cooling of all portions of the rotor blades in order to maximize the efficiency of the engine and prolong the life of the rotor blades.
It is therefore an object of the present invention to provide for a turbine blade with a cooling circuit that utilizes multiple metering and impingement cooling in order to increase the engine efficiency and improve the turbine blade life.